The present invention relates to a process for producing 2,2,2-trifluoroethanol (TFE) by catalytic hydrogenation of 2,2,2-trifluoroethyl trifluoroacetate with elemental hydrogen in the gaseous phase.
2,2,2-trifluoroethanol has a high thermal stability and, in certain mixture proportions with other materials, outstanding thermodynamic characteristics. Thus, it may be used in admixture with water as a working fluid in heat engines (for example, as "Fluorinol 85", a mixture of 85 mole percent, 2,2,2-trifluoroethanol and 15 mole percent water). Because of its special chemical properties, 2,2,2-trifluoroethanol may serve as a solvent (for example for polyamides and polypeptides) as well as a reactant (for example in the production of anesthetics). It can also be used as a reaction medium (for example, for photolytic reactions).
It is known that 2,2,2-trifluoroethanol can be produced by molecule cleaving hydrogenation of 2,2,2-trifluoroethyl trifluoroacetate with elemental hydrogen in the gaseous phase in the presence of catalytically active solid materials, that is to say by heterogenous catalysis. Two moles of alcohol are thereby produced from one mole of ester and two moles of hydrogen.
German Patent No. DE-PS 12 71 696 describes such a process which is carried out at temperatures between 225.degree. and 400.degree. C. and at pressures between 1 and 5 bar absolute, whereby either chromite solid catalysts or noble metal supported catalysts are utilized as the catalysts. Materials utilized as solid catalysts include, for example, copper chromite, zinc chromite, iron chromite and manganese chromite, or mixtures of oxides and chromites. The weight ratio of chromium oxide to other metal oxide may lie between 0.5:1 and 10:1.
Because known examples of noble metal supported catalysts produce only very low conversions or selectivity, only the chromite solid catalysts are relevant for practical economic application. However, contact with a catalyst material formed of chromium oxide and zinc oxide yields unsatisfactory results. The selectivity in particular may be increased by additions of copper oxide and calcium oxide (weight ratio of Cr.sub.2 O.sub.3 /ZnO=0.4:1 and Cr.sub.2 O.sub.3 /CuO=1.6:1). The relatively best results with reference to the catalyst life, conversion and selectivity are achieved with catalyst of chromium oxide, copper oxide and barium oxide (weight ratio of Cr.sub.2 O.sub.3 /CuO=1.1:1).
However, the required reaction temperatures of well above 200.degree. C. and the short lifetimes of at most 27 hours (with correspondingly low catalyst yields) are of little utility for technical applications. In addition, the use of such chromite catalysts with high chromium oxide contents is undesirable for a number of reasons (e.g. waste water disposal problems, carcinogenicity, etc.).
According to U.S. Pat. No. 4,072,726 a chrome-free, copper catalyst containing 50 to 100 weight percent copper oxide and 0 to 50 weight percent of an inert binder can be used to effect the same conversion under comparable temperature and pressure conditions. According to the examples given therein, at copper oxide contents between 75 and 95 weight percent and a reaction temperature of 235.degree. C., reaction times of 53 to 175 hours, conversions of over 54 percent and a selectivity of at least 95 percent are obtained. The corresponding catalyst yields lie between 19 and 42 kg of 2,2,2-trifluoroethanol per kilogram of catalyst.
Despite the substantially longer duration of the reaction and higher catalyst yields in comparison to the results of German Patent No. DE-PS 12 71 696, the required reaction temperatures, which likewise are significantly above 200.degree. C., and the extremely high copper oxide content, which leads to a notable increase in the cost of the catalyst, constitute disadvantages which cannot be overlooked.
High temperatures and high copper contents additionally increase the susceptability to thermal aging, for example by recrystallization and sintering, particularly when the synthesis gas contains traces of chlorine compounds (Ullman, Vol. 3, p. 545, 4th ed., 1976). This is, however, always the case in technical processes where the 2,2,2-trifluoroethyl trifluoroacetate is produced as initially described in U.S. Pat. No. 4,072,726 by reacting the corresponding acid chloride with 2,2,2-trifluoroethanol.